It is known that in the bone disease, "osteoporosis," there is a decrease in bone density and an increase in bone porosity which significantly weakens the bone structure. More specifically, there is a progressive loss of bone mineral matrix, together with non-ossified material, such that the bones become thin and brittle. The weakened bone is susceptible to fracture upon even minor impact. While the exact etiology of osteoporosis is not fully understood, it is known that the demineralization of bone tissue is widespread throughout the skeletal system. As will be appreciated by those skilled in the art, in bone formation, osteoblasts and fibroblasts generate collagen which is then mineralized by calcium phosphate which, in turn, is converted to hydroxyapatite. It is also known that cells known as osteoclasts play an important role in the resorption of bone. Under normal conditions, bone remodeling, i.e. formation and resorption, occurs in coupled cycles to maintain equilibrium of bone mass. Bone also serves as a reservoir of calcium which is utilized in numerous cellular processes. It is believed that serum calcium regulation is mediated by the actions of parathyroid hormone, vitamin B, calcitonin, and various other local and systemic hormones. However, even if a detailed understanding of the pathways involved in bone remodeling remains unclear, it is apparent that the origin of osteoporosis is related to cell dysfunction as opposed to merely mineral imbalance.
A number of factors are known to increase an individual's predisposition to osteoporosis. It is a disease associated with aging, occurring somewhat later in men than in women. One of the most significant predisposing factors is the onset of menopause. A significant percentage of elderly women are afflicted with osteoporosis. It often leads to spinal compression fractures and collapse of vertebral bodies which may produce a dramatic change in posture. Long bone and hip fractures often lead to fatal complications. While estrogen replacement therapy has been attempted for the treatment of osteoporosis, its safety represents a problem and its efficiency is in question. Other pharmacologic treatments have also been attempted such as calcium, vitamin D and calcitonin supplements, but none have proved successful. Therefore, it would be desirable to provide a method and apparatus by which osteoporosis could be treated without the need for drug therapy.
The study of osteoporosis has been severely limited by the lack of an adequate animal model. The most popular animal model at this time is the limb disuse model in which the sciatic nerve of an experimental animal is severed to bring about disuse of the lower extremities. This disuse produces atrophy and weakened bone structures which have been assumed by some to be somewhat similar to the weakened bone structures present in osteoporosis, since both osteoporosis and disuse atrophy lead to reduced bone mass. However, differences between the two conditions exist, and the reliability of this model as a treatment for osteoporosis has been questioned. Therefore, it would be desirable to provide a reliable animal model which more precisely follows true osteoporosis.
Mechanical devices have been employed to counter the effects of osteoporosis. This approach assumes that skeletal homeostacis, the process by which the fractional bone mass in an individual is maintained, is a function of mechanical stress and physical exercise. Indeed, in younger individuals, as well as in animals, it is known that decreased mechanical stress, as seen in disuse, immobilization, and most dramatically in astronauts in space flight, is related to increased bone resorption. However important this type of bone loss may be in younger individuals exposed to prolonged weightlessness in low-gravity environments, in bed-ridden immobilizations, or experimental animal models involving disuse atrophy, it remains clear that the onset and continuation of osteoporosis in older individuals is marginally connected, if at all, to exercise habits and is not reversible with programs of exercise.
In recent years, multidisciplinary investigations of developmental processes have provided evidence suggesting that electric and magnetic fields play an important role in cell and tissue behavior. In U.S. patent application Ser. No. 923,760, entitled, "Techniques for Enhancing the Permeability of Ions," which has been assigned to the assignee of the present invention and the disclosure of which is incorporated herein by reference, a method and apparatus are disclosed by which transmembrane movement of a preselected ion is magnetically regulated using a time-varying magnetic field. The fluctuating magnetic field is preferably tuned to the cyclotron resonance energy absorption frequency of the preselected ion. This important discovery brought to light the interplay of local geomagnetic fields and frequency dependence in ion transport mechanisms. It has now been discovered that by utilizing and extending the principles of cyclotron resonance tuning, an unexpected and remarkable advance in the control and modification of developmental processes in living tissue can be achieved. In U.S. patent application Ser. No. 172,268 filed Mar. 23, 1988, the inventors of the present invention disclose that cyclotron resonance can be used to control tissue development. In U.S. patent application entitled "Method and Apparatus For Controlling the Growth of Non-Osseous, Non-Cartilaginous, Solid Connective Tissue," filed Oct. 6, 1988, U.S. Ser. No. 254,438, the present inventors disclose a method of controlling the growth of non-osseous, non-cartilaginous, connective tissue which utilizes cyclotron resonance frequencies.
Still other art devices which broadly relate to non-invasive tissue control are typified by the devices disclosed in U.S. Pat. No. 3,893,462 to Manning entitled, "Bioelectrochemical Regenerator and Stimulator Devices and Methods for Applying Electrical Energy to Cells and/or Tissue in a Living Body" and in U.S. Pat. No. 4,105,017 to Ryaby et al. entitled, "Modification of the Growth Repair and Maintenance Behavior of Living Tissue and Cells by a Specific and Selective Change in Electrical Environment." These investigators have focused on the use of large pulsed magnetic fields to produce moderately high induced currents in living tissue with well-defined "therapeutic" waveforms. In U.S. Pat. No. 4,467,808 to Brighton, a non-invasive method of treating osteoporosis is disclosed which uses AC electrodes and high-frequency currents. It should also be noted that although a possible role of magnetic fields beyond the galvanic action of induced currents is briefly mentioned in U.S. Pat. No. 3,890,953 to Kraus et al., to Applicants' knowledge no investigator has previously controlled osteoporosis in the manner set forth in the present invention.